Documents FR 90 00550 and FR 2 771 148 already disclose such a disc brake piston cap in the form of a bellows-style dust boot housed in the annular groove at the end of the caliper, beyond the bore for the piston. This cap has a first outer fold of which the outer edge, which is also that of the cap, is fixed to the internal wall of the groove. The outer fold is followed by an intermediate fold and then by a penultimate fold and a last fold which is also the inner fold. The edge of the inner fold is housed in a groove of the piston. The known piston cap is able to move between a refracted position that corresponds to the retracted position of the piston, in which position the various folds are superposed, and a piston-deployed position in which the folds of the cap or boot are deployed axially and in a stepped manner between the groove of the caliper and that of the piston. The cap thus protects the surface of the piston and the bearing surface preventing contact with foreign bodies, liquid and dust.
This known piston cap comprises a re-folding aid to prevent the boot from tearing. This is because particularly when a brake pad is replaced, the piston is pushed back into its bore. It is possible that the cap will fail to fold back correctly in the groove of the caliper. It is then exposed to contact with the metal parts of the brake, the temperature of which may reach high values which, after a certain time, cause the boot to deteriorate. This boot, once torn, is no longer able to protect the inside of the piston against attack by liquid or solid matter, dust or the like.
The known cap depicted in FIG. 3 has five folds ranging from the small diameter to the large diameter: an outwardly directed inner fold 101, an inwardly directed intermediate fold 102, an outwardly directed intermediate fold 103, an inwardly directed intermediate fold 104 and finally an outwardly directed outer fold 105 and an overmoulded insert 106.